Abstract: In a method for frequency analysis of a signal of a hazard detector, wavelet transformation is combined with fuzzy logic analysis. In the transformation, based on orthonormal or semi-orthonormal wavelets, an original signal is fed to a multi-stage filter cascade of pairs of high-pass/low-pass filters. From the output of the high-pass filter, wavelet coefficients and values of the original signal, each filter stage produces an association function. The functions are normalized and analyzed further in accordance with fuzzy logic rules. The method is particularly suitable for analyzing signals from flame detectors, noise detectors and the like. As processor code for transformation and analysis is kept short, high speed and accuracy are achieved at low cost.

Abstract: In an optoacoustic gas sensor having a sensor body (1, 2), a light source (10), a measurement cell (6) with a gas-permeable membrane (15), a measurement microphone (13), and an optical measurement filter (11) between the light source (10) and the measurement cell (6), a reference cell (7) is included that is separate from the measurement cell (6). The reference cell (7) has a reference microphone (14) that is shielded against optoacoustic signals from the gas to be detected via the reference cell being substantially free from intensity-modulated optical radiation having an absorption wavelength of the gas to be detected. The measurement signal, which indicates gas concentration, is obtained by subtraction of the signals from the two microphones (13, 14).

Abstract: A passive infrared intrusion detector for the detection of infrared body radiation includes a sabotage detector, in particular for detecting spraying of the entrance window of the intrusion detector. The sabotage detector includes a light source, a corresponding light sensor, and an optical diffraction grating structure on the outside of the entrance window. The light source and the light sensor can be on the same or on opposite sides of the entrance window. By first- or higher-order diffraction, light from the light source is focused onto the sensor, and a resulting electrical signal from the sensor is evaluated by an evaluation circuit. In case of sabotage, the focusing effect of the optical diffraction grating structure vanishes, so that the light intensity at the detector is reduced. The drop in light intensity triggers a sabotage alarm signal.

Abstract: A surveillance device, e.g. a fire alarm or an intrusion detector, includes a mount having a connector block, and an insert having a sensor assembly, a printed circuit board with evaluation electronics, and an electrical contact to the connector block. The printed circuit board is a plug-in card with a contact strip. For insertion, with the mount disposed at a horizontal surface, for example, the insert is first moved vertically and then displaced horizontally. In the horizontal displacement, an electrical connection is established between the contact strip and the connector block.

Abstract: A serial data bus with a two-wire line and a plurality of bus nodes for the exchange of data messages in both directions between the bus nodes and a central unit connected to the bus and for the current supply of the bus nodes. Conflicts between data messages that appear simultaneously are resolved on the basis of the priority thereof. The bus is constructed in the manner of a multi-master system in which each bus and the central unit is a master, and the central unit provides the bus timing and controls the synchronization of the bus. Each bit transmission is divided up into a positive and a negative phase, the current supply of the bus nodes being effected in the positive phase and the data transmission being effected in the negative phase.The bus is preferably used for a hazard-detection system wherein the bus nodes comprise a micro-controller and either are constituted by special detectors with integrated bus or comprise an interface for the connection of the detectors.

Abstract: In a technique for detecting organic vapors and aerosols, e.g. of amines, hydrazines and nitrogen-containing compounds produced in combustion, molecules condense at a surface of a conductive device. By heating the conductive device in pulsed fashion, e.g. by resistance heating, condensed molecules are thermally ionized and emitted from the conductive device. Emitted ions are collected by a collector electrode, and the resulting ionic current pulse is amplified by a transimpedance circuit. The heat pulse lasts until the ionic current pulse has subsided, by which time the conductive device has become free of residual substances. As a result, the conductive device remains uncontaminated and has a long service life. The time-averaged power consumption of the technique is less than 2 mW. For resistance heating, a meander heater element can be disposed on a silicon nitride membrane across an etched opening in a silicon chip.

Abstract: The smoke detector includes a light source (1), a measurement section (3) with a measuring receiver (5), a reference section (2) with a reference receiver (4), and an analyzer circuit (6) connected to the receivers. The receivers are of like construction and receive like amounts of radiation from the light source (1). A difference signal (.DELTA.I) formed from the current signal (I.sub.r) of the reference receiver and the current signal (I.sub.m) of the measuring receiver is fed to the analyzer circuit. A reference current (I.sub.k) is superimposed upon the current signal (I.sub.r) of the reference receiver, and the light source is connected to a control circuit and regulated by the control circuit for compensation of the reference current (I.sub.k) by the reference current signal (I.sub.r). The difference signal (.DELTA.I) is superimposed with a compensation signal (I.sub.k ') for zero compensation.

Abstract: In a photo-acoustic gas sensor having a measuring cell, a lamp, a photo-diode, a gas-permeable diaphragm and a microphone, a device is included for monitoring the gas-permeable diaphragm and the microphone. The device is operated in an explosion-proof manner. Intentionally, for diagnostic purposes, an artificial pressure modulation is generated in the measuring cell. The pressure modulation is converted by the microphone into electrical monitoring signals which are amplified by an amplifier circuit and assigned to preset ranges by a microprocessor, for determining the functional condition of the diaphragm and the microphone, and of microphone sensitivity. Depending on the range assigned to the monitoring signal, an output signal is generated indicating a fault in the microphone and/or the diaphragm. In the event of long-term drift in microphone sensitivity, a calibration is performed in which gas concentration values are re-calculated and stored in an EEPROM.

Abstract: A fire alarm system comprises detectors with sensors for monitoring fire index quantities. The sensors generate corresponding sensor signals which are delivered to an analysis stage, in which the probability of a future false alarm is assessed and, if a defined magnitude of probability exists, an information signal is produced.

Abstract: A photo-acoustic gas sensor for measuring a gas concentration, e.g., of an explosive gas, consists of a cylindrical sensor body (1) which includes a cylindrical measurement chamber (13) whose longitudinal axis extends perpendicular to the longitudinal axis of the cylindrical sensor body. Without changing the outer dimensions of the sensor body, the length of the measurement chamber can be changed in accordance with a desired measurement sensitivity and a desired measurement range. A light source (5) is disposed such that it irradiates the measurement chamber without irradiating a gas-permeable membrane (2), so that the membrane will not produce an interference signal. The gas sensor is rendered explosion-proof as the light source and a photo-diode (6) which monitors the light source are tightly sealed from the environment. Proper functioning of a microphone (4), the light source and the photo-diode are monitored by analyzing a background signal.

Abstract: A fire detection system contains several detectors connected to a control center, some of which are fitted with at least two sensors for monitoring different fire parameters. Preferably, one sensor is a thermal sensor and another is an optical sensor. An arrangement for processing the sensor signals is located within each of the detectors. It contains a microcontroller for conditioning the sensor signals and for signal processing, with the aim of generating alarm signals. The alarm signals are obtained in a neural network.

Abstract: A structure-bone sound detector suppresses unwanted signals in a frequency range to be monitored, to enhance the immunity of the detector to false alarms. The output signal from a sound sensor undergoes preprocessing, and is then fed to a pair of comb filters that are connected in parallel. The comb filters have mirror image filtering characteristics. The filtered output signals from the two comb filters are provided to a minimum value stage, which selects the smaller of the two output signals. This selected signal is further processed to detect an alarm condition. With this arrangement, broad band signals of interest will produce approximately the same outputs from each of the two comb filters, and therefore be passed on for further processing. In contrast, a narrow band interference signal will be suppressed by one of the two comb filters, and therefore not selected for further processing.

Abstract: The infrared detector contains an emitter (4), a receiver (5) and an analysis circuit (2') for obtaining a working signal (Un). The analysis circuit (2') contains a controller (29) for outputting a compensating signal (Ik) superimposed over the incoming signal (Ie), which on the one hand receives the working signal (Un) and on the other hand is connected to the output of the receiver (5). The compensating signal (Ik) is selected so that the working signal (Un) is corrected to the value zero so that the maximum sensitivity is retained at all times.

Abstract: The motion detector generates a sensor signal (SS) which contains a direct current portion and an alternating current portion. The signal evaluation circuit (3) contains means for filtering out the direct current portion, an analogue-to-digital converter (4) and an amplifier for the alternating current portion of the sensor signal. The analogue-to-digital converter (4) is provided for the direct digitizing of the entire sensor signal (SS) and the means for filtering out the direct current portion are formed by a digital high-pass filter (5) connected downstream of the analogue-to-digital converter.

Abstract: In an infrared intrusion detector, a focusing mirror reflects incident infrared radiation of interest onto a pyroelectric sensor element. To prevent extraneous radiation from reaching the sensor element, the mirror has a reflective layer for reflecting infrared radiation of interest, and an absorptive layer disposed behind the reflective layer for absorbing extraneous radiation which has passed through the reflective layer. Infrared radiation of interest includes human body thermal radiation, and extraneous radiation includes the visible spectrum. Doped indium-tin oxide (ITO) is preferred for the reflective layer.

Abstract: The detector contains a structure-borne sound microphone connected to an electronic evaluation unit with a piezoelectric sensor (18) for structure-borne sound vibrations. This sensor has a vibrating bar (28), which is attached by means of hybrid technology to a carrier (27). The vibrating bar (28) is formed by a bimorph element and the carrier by an electrically conductive ceramic wafer.

Abstract: A flame is detected by signal analysis for intensity variations in radiation received by a sensor. A low-frequency spectrum of the signal is analyzed for mid- and cut-off frequencies, and the signal is classified as periodic or non-periodic. Periodic signals with a mid-frequency (.omega..sub.mp) above a first frequency value (G.sub.1), and non-periodic signals with a cut-off frequency (.omega..sub.gc) above a second frequency value (G.sub.2) are classified as interfering signals. The first frequency value is determined by the flicker frequency of a stationary flame having a magnitude corresponding to a flame of minimum magnitude to be detected. The second frequency value is selected greater than the first frequency value (G.sub.1).

Abstract: Upon insertion of a fire alarm insert into a corresponding fire alarm mounting, the insert covers the mounting. The insert has a movable fastening comprising a ring, for example, for fastening the insert to the mounting. Indicator elements are included for indicating proper positioning of the insert relative to the mounting.

Abstract: A protective coating for an electronic assembly on a circuit board is made from a pre-fabricated, roll-flattened plastic ribbon having desired pre-determined thickness. From the ribbon, a suitably shaped membrane piece is produced, e.g., by stamping or by water-jet cutting, with openings as may be desired for circuit components to be left uncovered. The membrane is placed onto the circuit board, softened by heating, and pressed on by means of a silicone stamp, for close contact with electronic modules to be protected. The membrane is then adhered to the circuit board by further heating. The starting material for the membrane is a mixture of a thermoplastic material and of a wax including a significant amount of branched-chain and cycloaliphatic hydrocarbons.

Abstract: A device (7) for testing the operation of smoke detectors (3) has a housing (1) which is open at one end and can be placed over the smoke detector (3). A test light source (5) in the housing provides light pulses which radiate into the inside of the smoke detector (3) under test. The test device also has a test light detector (4) that receives light coming from the smoke-indicating light source (15) of the smoke detector (3) and controls the test light source (5) in relation to the received light. The light pulse of the test light source (5) is received by the smoke-indicating light detector (14) of the smoke detector (3). By checking if the smoke detector (3) goes into the alarm state, it can be ascertained whether it is in an operational condition.